There has been a need of heat-exchanging plates, which are incorporated in heat-exchangers and the like, having high heat conductivity. In order to improve heat conductivity, it is desirable that the surface areas of the plates be increased by forming a fine recess and projections in the order of micrometers on the surfaces of the plates. As a method for transferring a fine recess and projections in the order of micrometers, a technology as described in, for example, Patent Literature 1 has been developed.
In the method for transferring to the surface of a metal plate described in Patent Literature 1, a transfer portion having a recess and projections formed on the outer peripheral surface of a transfer roller is pressed against a metal sheet, which is transported by rotation of transport rollers. Thus, a transferred portion having recessed and projecting shapes substantially similar to those of the transfer portion of the transfer roller is formed on the surface of the metal sheet.
Patent Literature 2 discloses a plate-type heat exchanger. In this plate-type heat exchanger, plate sets and bulkhead plates are alternatingly stacked. The plate sets each are formed of two plates, which each have a row of openings arranged in a specified pattern, are superposed on each other such that the rows of openings of the two plates cross each other. The bulkhead plates each have communication holes at four corners thereof. The plate-type heat exchanger is disclosed, in which circulation layers for a fluid are defined by the bulkhead plates and each of the circulation layers stacked in an up-down direction communicates with the every other circulation layers. In order to improve heat conductivity and strength, a heat-exchanging plate used for the heat exchanger has, for example, chevron-shaped grooves known as “herring-bone” having a height of smaller than 10 mm to smaller than 10 cm press-formed thereon. After that, the heat-exchanging plate is incorporated in the heat exchanger.